Rem sleep frequency and amplitude relationship

The first four stages of sleep are NREM sleep, while the fifth and final stage of sleep Theta waves are even lower frequency (4–7 Hz), higher amplitude brain waves . There was a significant positive correlation between the degree to which. A diffuse decrease in amplitude was observed for both frequency ranges. White dots Relationship with low-frequency oscillations of NREM sleep. We then. Both wake and REM sleep theta share a similar frequency range and . () reported a positive correlation between both peak frequency and amplitude of.

Conversely, disrupting sleep through repeated awakening only impaired extinction if awakenings occurred during REM sleep, but not if they occurred during NREM sleep Spoormaker et al. In addition to supporting fear extinction, REM sleep was found to predict post-sleep recognition of negative emotional pictures Nishida et al.

Administration of hydrocortisone during sleep following an emotional memory task resulted in superior recognition for emotional vs. Although sleep was not recorded in this study, the observed strengthening of emotional memory could be related to cortisol-mediated processes during REM sleep, as cortisol levels are naturally elevated during REM compared to NREM sleep Steiger, Areas implicated in memory processing during wake, in particular limbic circuits within the medial temporal lobe, are highly active during REM sleep Maquet et al.

At a cellular level, Pavlides and Winson observed reactivations of hippocampal neurons active during prior wakefulness during subsequent REM sleep. Even at a molecular level—plasticity-related gene expression increases within the hippocampus during REM sleep Ribeiro et al.

A recent study from the same group compared mRNA levels of plasticity-related genes within the hippocampus following either exposure to a novel or familiar control environment Calais et al.

There was also no upregulation of plasticity-related gene expression in rats who had not been exposed to the novel environment. A further recent study also revealed that increasing REM sleep amount through REMSD-induced rebound up-regulated the expression of plasticity-related transcription factors within the hippocampus Ravassard et al.

A distinct role for REM sleep in memory is also supported by the striking similarities and contrasts between neuromodulator states in REM sleep and wakefulness. The wake-like levels of acetylcholine in the limbic system suppress excitatory feedback potentials within the hippocampus and in the cortex Hasselmo and Bower, During wake, this is thought to promote memory encoding by allowing the formation of new memory traces within the hippocampus without interference from previously stored memory traces Hasselmo, Noradrenaline has been shown to suppress excitatory feedback transmission within the somatosensory and piriform cortex Dodt et al.

While wake is characterized by both high acetylcholine and noradrenaline levels, in REM sleep only acetylcholine is raised. As a consequence, excitatory feedback within the neocortex would remain uninhibited during REM sleep Hasselmo,while hippocampal afferent inputs would be suppressed Marrosu et al.

Based on these neuromodulator states, it has been proposed that during REM sleep, memories within the neocortex—free from interference from the hippocampus—recombine and potentially integrate into existing memory networks between periods of NREM sleep-dependent memory consolidation Hasselmo, ; Walker, ; Walker and Stickgold, ; Sterpenich et al. Functional neuroimaging studies reveal significantly increased activation in the amygdala, striatum, hippocampus, medial prefrontal cortex and insula, which are areas strongly associated with emotional processing in wake Nofzinger, ; Miyauchi et al.

The heightened activity within the limbic system in particular Maquet et al. Possibly as a consequence of its emotional physiology, REM sleep is unique for its comparably emotional dreams Hobson et al.

REM Sleep and Emotional Arousal In addition to a general role of REM sleep in emotional memory processing, a separate line of research has emerged concentrating on a more specific link between REM sleep and the modulation of emotional responses. Whether this role is part of the same mechanism, or relies on distinct processes is unclear and needs to be investigated more systematically.

This section reviews evidence specifically linking emotional response modulation and REM sleep. Thus pathological REM sleep may underlie some of the symptoms of mood disorders Walker and van der Helm, Even in mice models for depression i. Experimental Evidence for a Role of REM Sleep in Emotional Regulation Some evidence suggests a sleep-dependent decrease in both subjective emotional arousal and autonomic response to negative stimuli compared to an equally long period of wake in humans Gujar et al.

In line with this notion, sleep-dependent habituation was only observed across naps containing REM sleep, not across naps consisting solely of NREM sleep Gujar et al. In contrast, Groch et al. In a further study, participants rated emotional stimuli as more negative across late sleep compared to early sleep Wagner et al. Similarly, subjective emotional arousal went down across wake and was maintained across sleep Baran et al. The degree of arousal maintenance was associated with greater time spent in REM sleep.

REM sleep amount also predicted an increase in autonomic response in the form of skin conductance to emotional images shown before and after sleep Baran et al. Thus it appears that REM sleep may modulate emotional arousal, however the direction of this change may depend on other yet to be determined factors, such as the nature of the emotional stimuli, the stress experienced during the task or possibly the involvement of memory Genzel et al.

Theta Activity Theta activity describes synchronized oscillating local field potentials of neuronal populations within the range of 4—10 Hz initially observed in rodents Siapas et al. Although humans also display a distinct 4—10 Hz hippocampal activity during both active wake Burgess and Gruzelier, ; Ekstrom et al. Similarly to the theta activity observed in rodents, human slow theta hence forward referred to simply as theta activity also occurs in the human hippocampus during both wake and REM sleep Moroni et al.

The possible explanation for humans having a slower version of theta activity is the larger brain size which may require slower oscillations to travel greater distances between brain regions Moroni et al. Accordingly, a slower hippocampal theta activity is also seen in dogs, cats, and monkeys Lega et al. Theta Generation and the Role of Acetylcholine in Rats Hippocampal theta activity appears to originate from nuclei within the brain stem which project via the hypothalamus to the septal complex comprising of the medial septum and a subregion of the Broca area Pignatelli et al.

The septal complex, in turn, projects to the hippocampus via the fimbria-fornix pathway. The medial septum contains pacemaker cells which fire at theta frequency Dragoi et al. Some of these pacemaker cells release acetylcholine Mesulam et al.

Inhibiting medial septum cell activity though targeted injection of lidocaine Winson, or muscimol Bland et al. Both acetylcholine and GABA jointly contribute to generating theta, as reductions of either leads to partial but not complete abolishment of theta power Yoder and Pang, ; Li et al. Given the strong link between acetylcholine and theta activity, the role of acetylcholine in memory processes within the hippocampus is highly indicative of the function of theta activity.

It appears that high levels of acetylcholine enhance memory encoding during wakefulness, yet do not affect retrieval in a range of learning tasks in both rats and humans for a review, see Hasselmo, Early work in rats showed that blocking acetylcholine through muscarinic antagonists such as scopolamine disrupted memory encoding if the drug was administered prior to learning, as opposed to during the gap between learning and recall Ghoneim and Mewaldt, In humans scopolamine also disrupted encoding of memories without affecting retrieval Atri et al.

Thus it appears acetylcholine is only involved in the encoding though not the consolidation of novel hippocampal memory traces during wake. This has enticing implications for investigating the function of REM sleep, during which hippocampal acetylcholine levels exceed those of wake. This would suggest encoding-related processes occur during REM sleep—in stark contrast to the acetylcholine-independent memory consolidation processes occurring during NREM sleep.

The specific role of theta activity in this is thought to be the binding of disparate brain regions during encoding and retrieval Vertes, Physiological evidence strongly supports a role of hippocampal theta activity in rats in the formation of novel memories during wake.

Thus seminal in vitro work by Huerta and Lisman demonstrated that a priming pulse four pulses delivered at Hz induces LTP in the hippocampal CA1 of a brain slice only if the pulse arrives at the peak of carbachol-induced theta activity defined by the authors as 5—12 Hz. Taken together, this suggests both spatially and temporally differential theta-driven plasticity within the hippocampus. Behavioral evidence in rats also supports a role of hippocampal theta activity during wake in memory encoding.

Thus hippocampal theta power during encoding predicts the success of later recall Berry and Thompson, ; Seager et al. It appears not only the presence, but also the timing of learning with relation to theta is important in determining the success of encoding. Thus, the rate of learning in rabbits is fastest when hippocampal theta power is at its peak Berry and Thompson, Also in rabbits, the rate of conditioning to a stimulus is increased in both delay Seager et al.

Human studies are comparatively scarce, given that hippocampal theta activity can only be recorded intracranially in epileptic patients. Whereas neocortical theta range 4—8 Hz activity reliably predicts encoding, working memory and navigation for a review, see Kahana et al.

They reported peak activity around 3 and 8 Hz within the hippocampus. While the power of 3 Hz activity increased during successful encoding trials, 8 Hz activity displayed an inverse relationship.

Furthermore, 3 Hz power was correlated with hippocampal gamma power. From this, the authors concluded that delta range 3 Hz activity within the hippocampus—similarly to the slower theta observed in humans during REM sleep—is the human analog to rodent hippocampal encoding-related theta activity.

Both frequencies were synchronized between the hippocampus and the temporal cortex, suggesting hippocampal-cortical communication. Somewhat different results were reported by Rutishauser et al. The following section will highlight the similarities and differences between wake and REM sleep theta activity. Theta activity in both states is associated with the burst-like discharge of acetylcholine—which is strongly linked with plasticity—within the basal forebrain Lee et al.

There is however some evidence that wake and REM sleep theta differ in their generation and function. Firstly, a genetic mutation in mice was found to slow down hippocampal theta frequency defined as 5—9 Hz in REM sleep, but not in wake Tafti et al.

Rapid eye movement sleep - Wikipedia

This particularly applies to the coupling between theta and fast gamma — Hzwhich is ninefold stronger in REM vs. Taken together, this suggests that—at least in rodents—wake and REM sleep theta differ in either their generation mechanism or regulation and may serve distinct, though possibly related functions.

REM Sleep Theta and Gamma Coupling Rapid-eye movement sleep theta activity appears to also modulate higher frequency activity in the brain. Thus, theta—gamma phase coupling during REM sleep within the hippocampal CA1 region in rats was found to be distinct for slow, mid-frequency and fast gamma Belluscio et al.

Gamma amplitude within these three bands was found to be modulated by theta phase. Phase-phase coupling was only detected between theta and slow and mid-frequency gamma, though not between theta and fast gamma. The authors interpreted this finding as suggesting an intricate multiple time-scale control of neuronal spikes during REM sleep, supporting information transfer and spike timing-dependent plasticity. Therefore as different bands of gamma are coupled differentially to the phases of theta between wake and REM; REM sleep could effectively represent a reweighting of the items which are stored during wakefulness.

These cells have been found across several species including humans Ekstrom et al. This multi-faceted representation has led to the suggestion that they encode episodes structured in space or episodic memory on the single neuron level.

Including and excluding spatially modulated cells, distinct classes of cells within the hippocampal formation i. Furthermore individual cells in the hippocampus fire at different phases of theta in novel vs. Hasselmo proposed this phasic difference can act as a switch between encoding and retrieval of memories during wake.

In REM sleep however, such a phase shift of cell firing could prioritize novel or emotionally salient memories while offloading the hippocampus of memories with less novelty or emotional salience. A possible indicator of such reorganization is provided in the work of Grosmark et al. This temporally coordinated firing of place cells takes place at a fold faster rate than experienced during traversal of the environment.

These events occur in both quiet wake Foster and Wilson, ; Jackson et al. Temporally coordinated activity of place cells preceding experience in a novel unexplored environment Dragoi and Tonegawa, has also been demonstrated, this phenomenon occurs before experience of the environment and therefore could underlie prospective planning by rehearsing and strengthening possible future trajectories.

Pertinent to our discussion, these sequences could also encode emotional salience, as reactivations leading to remembered goal reward locations appear to be preferentially activated during wake SWRs Pfeiffer and Foster, Sequences associated with previously unexplored rewarded vs. Critically, coordinated sequential activity of hippocampal place cells also occurs during REM sleep Louie and Wilson, and thus in the presence of theta and absence of SWRs.

Interestingly, REM sleep appeared to only reactivate sequences previously activated during exploration of a familiar track, though not sequences associated with a novel environment. Although the sample sessions of REM sleep analyzed were few 15 REM episodes ; this could be due to lower quality post-behavioral sleep following novelty.

These pieces of evidence clearly implicate the role of REM sleep in recapitulating wake experiences in terms of the sequential firing of individual neurons.

Though there are no human studies investigating sequential reactivation of place cells during REM sleep, the phenomenon of cued-memory reactivation during sleep both during SWS and REM sleep supports the idea that memories are reactivated during both sleep stages.

The role of REM sleep theta activity in emotional memory

Thus, sound cues associated with Morse code presented during REM sleep resulted in improved performance following sleep, though only if cueing occurred during phasic—not tonic the distinction is elaborated further on —REM sleep Guerrien et al. In a separate study, participants were exposed to a loud ticking alarm clock while learning a set of complex rules Smith and Weeden, Exposure to the same sound during following REM sleep led to a significant improvement in performance at a 1 week follow-up test compared to a non-cued group.

Sequential reactivations of cell assemblies representing experienced space are a clear candidate for stored memories. The fact that these occur during REM sleep — in coordination with ongoing theta activity — and that these reactivations are biased by exposure to memory cues during REM sleep — provides a strong case for REM sleep having a role in the processing of these memories.

PGO waves are large mV field potentials which propagate from the pontine tegmentum, to the lateral geniculate nuclei of the thalamus and the occipital cortex Nelson et al. PGO waves during REM sleep in rodents have been repeatedly linked with emotional memory consolidation. While suppressing PGO wave generation in rats impaired avoidance memory retention across sleep Mavanji et al. It appears the quality of PGO wave activity is directly related to memory processes, thus a number of studies have reported an increase in PGO wave density following fear memory training in rats which predicted overnight strengthening of the memory Datta, ; Datta and Saha, ; Ulloor and Datta, ; Datta et al.

Furthermore, post-training PGO wave density was associated with increased activity of brain-derived neurotrophic factors and plasticity-related immediate early genes in the dorsal hippocampus Ulloor and Datta, ; Datta et al.

Selective elimination of PGO wave generating cells prevented these increases, while enhancing PGO waves through cholinergic activation of these cells augmented the increases. Thus, it has been proposed that PGO waves enhance synaptic plasticity in areas they pass through Datta et al.

It appears both are driven by theta oscillations.

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Conversely, when PGO waves are elicited through audio stimulation, theta phase is not reset, though PGO waves eventually become phase locked with theta again Karashima et al. In a further study, Karashima et al. The same group also found that in both cats and rats, theta frequency accelerates several ms prior to the negative peak of PGO waves Karashima et al.

When PGO waves are inhibited by lesions to the subcoeruleus region, where PGO waves are generated, synchronization between regional theta waves is disrupted.

Critically, PGO wave density also reflects theta synchronization between the hippocampus and amygdala during REM sleep in rats Karashima et al. However, based on fMRI evidence, the pontine tegmentum, thalamus, primary visual cortex, putamen, and limbic areas activate in synchrony with the occurrence of REMs, which strongly suggests a similar activity in humans Wehrle et al.

REM density has been observed to increase following stressful periods of learning—based on University students during an exam preparation Smith and Lapp, This could reflect the enhanced processing of emotional memories i. In waking humans, the same injections produce paradoxical sleep only if the monoamine neurotransmitters have already been depleted.

REM-on neurons are primarily cholinergic i. They are also shorter in duration and more likely to loop back to their starting point. About seven of such loops take place over one minute of REM sleep. In slow-wave sleep the eyes can drift apart; however, the eyes of the paradoxical sleeper move in tandem.

Congenitally blind people, who do not typically have visual imagery in their dreams, still move their eyes in REM sleep. Heart ratecardiac pressure, cardiac outputarterial pressureand breathing rate quickly become irregular when the body moves into REM sleep. Overall, the brain exerts less control over breathing; electrical stimulation of respiration-linked brain areas does not influence the lungs, as it does during non-REM sleep and in waking.

In females, erection of the clitoris nocturnal clitoral tumescence or NCT causes enlargement, with accompanying vaginal blood flow and transudation i. During a normal night of sleep the penis and clitoris may be erect for a total time of from one hour to as long as three and a half hours during REM. However, even cats with pontine lesions preventing muscle atonia during REM did not regulate their temperature by shivering. When the body shifts into REM sleep, motor neurons throughout the body undergo a process called hyperpolarization: Muscle inhibition may result from unavailability of monoamine neurotransmitters restraining the abundance of acetylcholine in the brainstem and perhaps from mechanisms used in waking muscle inhibition.

Certain scientific efforts to assess the uniquely bizarre nature of dreams experienced while asleep were forced to conclude that waking thought could be just as bizarre, especially in conditions of sensory deprivation. The prospect that well-known neurological aspects of REM do not themselves cause dreaming suggests the need to re-examine the neurobiology of dreaming per se. People awakened from REM have performed better on tasks like anagrams and creative problem solving. REM sleep through this process adds creativity by allowing "neocortical structures to reorganise associative hierarchies, in which information from the hippocampus would be reinterpreted in relation to previous semantic representations or nodes.

In the ultradian sleep cycle an organism alternates between deep sleep slow, large, synchronized brain waves and paradoxical sleep faster, desynchronized waves.

Sleep happens in the context of the larger circadian rhythmwhich influences sleepiness and physiological factors based on timekeepers within the body. Sleep can be distributed throughout the day or clustered during one part of the rhythm: Many animals and some people tend to wake, or experience a period of very light sleep, for a short time immediately after a bout of REM.

Rapid eye movement sleep

The relative amount of REM sleep varies considerably with age. The first REM episode occurs about 70 minutes after falling asleep. Cycles of about 90 minutes each follow, with each cycle including a larger proportion of REM sleep.